I have the bead shaping done on the new metal. My Problem is how many inches should I allow when I cut the old metal out? The metal on the truck is in great shape. The beading all around is rotted only half way. This is my first try on patch panels so I would appreciate some suggestions. Thanks ahead of time.1938 Ddg Hmpbck BEST Profile 6 26 04 002.jpg

That looks like a nice project.
I would say it depends how far in the rust goes; would try to determine where the sound metal is and go from there. It looks like it would be a few inches away from the beltline or bead to me. The rear corner is the same.
How large are the patch panels? do you have any photos?

All depends on ease of access from behind the panel, for finishing. If access is easy, then only take out all the bad metal, and try to finish off on flat areas or ones with curvature to prevent or minimise distortion.

Thanks for your answers. The metal is in great shape just a few inches above the beading. I first thought of replacing the whole side at the body crease in the middle. So I beaded a whole panel on one sheet of 18 ga sheet. Then when I thought about handling the whole bottom side of the truck, I had second thoughts. So I ask for other opinions. Thanks